Kashuba A. Transformation of electronic energy structures and optical parameters of substitutional solid solutions of halides indium and thallium

The thesis is devoted to the systematic experimental and first principles investigation of structural, electronic, optical and mechanical properties of InxTl1-хІ substitution solid solutions. A series of InxTl1-xI (x = 0.4 – 0.9) single crystalline solid state alloys were successfully synthesized by the vertical Bridgman- Stockbarger method. For the first time the density functional theory based band structure calculations are performed and features of the band energy dispersion are discussed. Also the origin of the principal valence and conduction bands is explored. The dependence of relative linear expansion of InxTl1–хI crystals (Т = 300–520 K) has been obtained. Based on this, the temperature dependence of thermal-expansion coefficient α has been found. Dependence of birefringence Δni on temperature and concentration of the TlI component in the solid solution has been studied. Elastic properties of substitutional solid solutions InxTl1–хI have been studied. The corresponding Young modulus, shear modulus, and compression modulus are calculated theoretically. The dependence of the elastic properties of the InxTl1–хI solid solution on the content х within the interval 0.375 ≤ х ≤ 1 is analyzed. The velocity of sound propagation in examined specimens is studied experimentally. The obtained data are used to calculate the elastic coefficient С22. Features of the photoconductivity spectra for different crystallographic directions have been discussed with taking into account the chemical bonds anisotropy. Excitation and emission spectra of the photoluminescence of synthesized In0.5Tl0.5I solid solution are measured and analyzed.